Rectum and Anal Canal Flashcards
Is the rectum retro, intra, or secondary retroperitoneal ?
Partially retroperitoneal
− Has mesorectum, NOT mesentery
Describe the anatomical path of the rectum.
1) Begins in front of the 3rd sacral vertebra
2) Follows the curve of the sacrum and coccyx
3) Ends in front of the tip of the coccyx by piercing the pelvic diaphragm and becoming continuous with the anal canal
Describe the main structural components of the rectum.
- Has lateral curvatures, coinciding with rectal folds or valves internally
- The lower part of the rectum is expanded to form the rectal ampulla
- Pararectal fossa on both sides
- Lacks taenia, haustra or epiploic appendices
- Inside there are 3 transverse mucosal folds which do not disappear when rectum is distended
What is the main function of the rectum ?
Storage of faeces prior to defecation
At which levels are the mucosal folds of the rectum found ?
5-6 cm from anus
8-9 cm from anus
11-13 cm from anus
What is the junction between anus and rectum called ? How is it formed ?
Perineal flexure (anorectal junction or angle)
Caused by anterior pull of the rectum by puborectal muscle
State the main anatomical relations of the rectum in the male.
- Bladder (anteriorly)
- Prostate (palpable per rectum) (anteriorly)
- Rectovesical pouch (anteriorly, between rectum and bladder)
- Rectoprostatic fascia (Denonvillier’s fascia) (anteriorly, between rectum and prostate)
- Pelvic plexus (at risk in rectal surgery) (laterally)
- Seminal vesicles (anterolaterally)
- Ductus deferens (anterolaterally)
- Ureter (anterolaterally)
State the main anatomical relations of the rectum in the female.
- Bladder (anteriorly)
- Uterus (anteriorly)
- Rectouterine pouch (of Douglas) (anteriorly, between rectum and uterus)
- Rectovaginal fascia (anteriorly, between rectum and vagina)
- Pelvic plexus (at risk in rectal surgery) (laterally)
- Ureter (anterolaterally)
How far are rectouterine, and rectovesical pouches from the anorectal angle respectively ?
Rectouterine pouch (of Douglas): 5.5 cm above anorectal angle Rectovesical pouch: 7.5 above anorectal angle
How long is the anal canal ?
Approximately 4cm long
Where does the anal canal start, and finish ?
From the pelvic diaphragm to the anus
State the main anatomical relations of the anal canal.
Related to ischioanal fossa laterally
Identify the main muscles surrounding the anal canal.
- Surrounded by levator ani, external anal sphincter and internal anal sphincter
- The anorectal ring is a muscular structure at the junction of the anal canal and the rectum.
Identify the main components of the anorectal ring.
It includes the puborectalis sling and upper portions of the internal and external sphincters.
What are possible clinical consequences of abnormalities of the anorectal ring ?
Division of the anorectal ring results in incontinence.
What kind of muscle makes up the internal anal sphincter ? Where does this sphincter end ?
− Smooth muscle, autonomic
− Derived from circular muscle layer
− Ends at intersphincteric groove
What kind of muscle makes up the external anal sphincter ? Where does this sphincter end ?
− Striated muscle
− One functional unit with deep, superficial and subcutaneous parts
− Fuses with puborectalis
Describe the main structural components of the anal canal.
♣ Below anorectal line, in the upper part of the anal canal, there are 8-10 longitudinal folds called anal columns (formed primarily by branches of the superior rectal vein, but also superior rectal artery, lymphatics, and nerves) (in the hemorrhoidal zone)
-Some of the columns are bigger than the others. These are called anal cushions, usually at 3, 7, 11 o’clock in the lithotomy position. These cushions help sphincters close the lumen.
♣ Anal columns unite with each other inferiorly and form anal valves
♣ Superior to each valve is a depression termed an anal sinus (crypt), which contain mucous glands
♣ The anal valves together form a circle in the anal canal called pectinate (dentate) line (where the anal membrane was in the fetus)
- Superior to the pectinate line is the hemorrhoidal zone (area of anal columns)
- Inferior to the pectinate line is a transition zone known as the anal pecten
♣ Anal pecten ends inferiorly at the anocutaneous line (“white line”), or where the lining of the anal canal becomes true skin (below that line is the cutaneous zone)
For a diagramatic representation of this, refer to slide 18 in lecture.
What is the function of the mucous glands present in the crypts superior to the anal valves ?
Lubricate the feces
Describe the nerve supply of the anal pecten.
Supplied by inferior rectal nerve
Sensitive to pain, temperature, touch, pressure
Describe the arterial supply of the rectum and anal canal.
SUPERIOR 1/3: inferior mesenteric artery
→ Superior rectal artery
MIDDLE 1/3: internal iliac
→ Middle rectal artery (variable, sometimes absent)
BELOW ANORECTAL LINE: Internal pudendal
→Inferior rectal artery
May be contribution form median sacral
What is the clinical significance of the median sacral artery possibly contributing to the arterial supply of the anal canal and rectum ?
A contribution from the median sacral may cause bleeding during surgery
Describe the veinous drainage of the rectum and anal canal.
1) Internal (submucosal) Rectal Plexus:
− Drains to superior rectal vein
2) External Rectal Plexus:
a. Superior 1/3: Superior rectalinferior mesenteric →
Hepatic portal vein
b. Middle 1/3: Middle rectal → internal iliac + internal pudendal veins
c. Inferior 1/3: Inferior rectal → internal iliac + internal pudendal veins
Where are the internal, and external rectal plexuses found respectively ?
Internal rectal plexus
− In submucosa
External venous plexus
− Between and outside muscle layer (i.e. between and outside sphincters)
Describe the lymphatic drainage of the rectum and anal canal.
General path is: Epicolic (along the wall) → paracolic (along the vessels) →intermediate (ın mesorectum) → principal lymph nodes.
The principal lymph nodes for:
1) Superior rectum→ Inferior mesenteric nodes
2) Inferior rectum and proximal anal canal →Internal iliac nodes
3) Distal anal canal → Superficial inguinal nodes
Describe the nerve supply of the rectum and anal canal.
PARASYMPATHETIC from S2-4 via pelvic splanchnic nerves →pelvic (inferior hypogastric) plexus
− Increases peristaltism
− Relax anal sphincter
− Visceral senses
SYMPATHETICS from L1-2(3) via lumbar splanchnic nerves
− Contract anal sphincter
SOMATIC nerves from S2-4→ pudendal nerve
− Supplies external anal sphincter, adjacent pelvic floor muscles (puborectalis)
SOMATIC afferent below the pectinate line of the anal canal is pudendal nerve
Identify possible causes of hemorrhoids.
Due to blockage of drainage of hemorrhoidal plexus (AKA internal and external rectal plexuses), possibly due to:
- Portal hyperT
- Tumors
- Pregnancy
- Chronic constipations (perhaps due to low fiber diet)
- Sedentary life
What are the main kind of hemorrhoids ?
Internal haemorrhoids- internal plexus involved
External haemorrhoids- external plexus involved
Describe how fecal continence occurs, naming all the structures responsible for this.
- Levator ani and puborectalis, making rectoanal angle more acute; internal and external anal sphincters; abdominal pressure flattens anterior wall of lower rectum over upper anal canal; anal cushions close the canal
- The rectum can partially fill without an increase in pressure (c.f. bladder); the anal canal sensation (specialised receptors) can allow the cortex to distinguish between gas, fluid and solid faeces; there are stretch receptors in levator ani and the tissue around the anal canal
- Eventually, rectal pressure forces its contents into the anal canal, but defecation is prevented by learned cortical inhibition; only gas may be allowed to escape; the external anal sphincter forces faeces back up in to the rectum
Describe the nervous processes involved in defecation.
When defecation is allowed:
♠ Cortical inhibition is released, via the corticospinal tracts (like micturition)
♠ Abdominal pressure is increased
♠ Puborectalis relaxes allowing the rectoanal angle to straighten; the external sphincter anal splinter relaxes (somatic S2, S3, S4)
♠ The lower colon and rectum contract while the internal anal sphincter relaxes (parasympathetic pelvic splanchnics S2, S3, S4 via pelvic plexus)
♠ The reflexes are therefore at S2, S3, S4
♠ Incontinence: Loss of control following cortical or cord lesions above S2, S3, S4; or damage to the external anal sphincter during obstetric or perineal procedures; or entrapment of the pudendal nerve
